Abstract

Arachidonic acid metabolites such as prostaglandins, thromboxanes, and leukotrienes are well known modulators of intestinal vascular perfusion, motility, and electrogenic ion transport. We investigated the effect of different hydroxyeicosatetraenoic acids (HETEs) from cytochrome P450- and lipoxygenase-dependent arachidonate metabolism on electrogenic chloride secretion in rat distal colon. Using conventional Ussing techniques, basolateral 12-HETE significantly decreased basal short-circuit current (I_sc) and inhibited furosemide-sensitive Cl⁻ secretion stimulated by either dibutyryl cAMP, prostaglandin E₂, or theophylline in a concentration-dependent manner (IC₅₀ = 1.5 nM). These data were underlined by significant inhibition of J_net^Cl in unidirectional ³⁶Cl flux measurements. Direct regulation of the basolateral Na⁺-K⁺-2Cl⁻ cotransporter or the Na-K-ATPase could be excluded because 12-HETE had no effect on furosemide-sensitive K⁺ secretion induced by epinephrine, or ouabain-sensitive Na⁺ reabsorption stimulated by aldosterone. Inhibitors of Ca²⁺-activated and voltage-gated K⁺ channels such as apamin, charybdotoxin, and dendrotoxin did not affect secretagogue-dependent I_sc and its regulation by 12-HETE. In contrast, glibenclamide significantly attenuated the effect of 12-HETE on secretagogue-induced I_sc, whereas chromanol 293B, an inhibitor of cAMP-dependent K⁺ conductance, had an additive effect. We speculate that 12-HETE, like glibenclamide, affects intestinal Cl⁻secretion by inhibiting basolateral K⁺_ATPchannels. In contrast to these findings, neither 5-HETE nor 20-HETE had any effect on basal I_sc or cAMP-dependent Cl⁻secretion.